A growing number of facilities providing screening mammography have information systems which allow them to track the reasons for and results of every mammogram performed. A growing concern about mammography quality has led to interest among radiologists practicing in the community in documenting their rates of false positive and false negative mammogram, and in understanding the reasons for erroneous interpretation. Documentation of false positive requires follow-up which is relatively easily completed by mammographers. However, documentation of false negative examinations requires identification of all breast cancer cases among patients seen at the mammography facility, not just the cancers detected by mammography. Linkage with a tumor registry greatly facilitates such identification. to address this need, routine linkage of a community mammography registry with a high-quality tumor registry is proposed. The linked mammography-tumor registry (MTR) will provide a database to support epidemiologic, and potentially basic, research on breast cancer detection by investigators at the Fred Hutchinson Cancer Research Center. Reporting for quality assurance and surveillance purposes will be carried out routinely. Collaboration with radiologists, surgeons, pathologists, and oncologist practicing in the community is emphasized. The specific aims are to: 1) Demonstrate the feasibility of developing and maintaining a community MTR by a) specifying data items to be collected, and data quality control procedures to be used, by mammography facilities participating in the MTR; b) linking an existing community mammography database with an existing tumor registry; and c) expanding the MTR to additional communities within Washington State. 2) Demonstrate the usefulness of the MTR by conducting four analyses to investigate a) the performance of mammography in the community; b) the relationship of breast density to risk of detection as an interval cancer, c) the relationship of breast density to risk of cancer detection after it has spread beyond the breast density to risk of cancer detection after it has spread beyond the breast; and d) the relationship of post- menopausal hormone use to density of breast tissue. 3) Explore the feasibility and usefulness of enhancing the MTR for research purposes by actively involving community pathologists, surgeons, and oncologist, in its development and use.